A memory ballooning technology is for adjusting an allocation amount of a memory, by performing collection/allocation of the memory allocated to a virtual machine. For example, a virtualization control unit providing a virtual machine determines that the memory is overcollected, based on occurrence of a swap within the virtual machine and a monitoring result of the virtual machine. Further, there is a technology in which the virtualization control unit executes cancelling of the collection of the memory from the virtual machine or allocation of the memory (for example, PTL 1).